The present invention relates to an X-Y plotter of the type wherein drawings and/or other graphics are drawn by a pen onto paper supported by a support surface with which the pen is associated, and deals more particularly with a means for supplying pressurized air to a reservoir holding ink used by the pen to achieve an acceptable flow of ink from the pen during a drawing procedure and with a means for indicating when the ink reservoir is out of ink.
Pen plotters, particularly those using ball-point pens or capillary tube pens, have long been recognized as having potential problems in obtaining an adequate flow of ink from the pen to achieve the drawing of continuous lines without the appearance of gaps or weak line portions. This problem has been solved, or greatly reduced, in many instances by pressurizing the ink supply to the pen either by directly pumping the ink itself, by supplying the ink in a pre-pressurized capsule, or by providing a refillable ink reservoir pressurized by an overlying volume of pressurized air. In the latter case the air for pressurizing the reservoir is typically supplied to it by an air pump driven by its own separate motor. The use of a separate motor for the air pump, however, adds cost and complexity to the plotter, and the pump itself is often of greater capacity than required and otherwise not well suited to its application.
Also, if the ink in the ink reservoir becomes all used up, the pen will naturally fail to draw acceptable lines due to lack of ink, and some means should be provided to warn of an out of ink condition and/or to prevent further operation of the plotter when such condition arises.
The general object of this invention, is, therefore, to provide a plotter of the aforedescribed type wherein the ink is supplied to the pen from a refillable reservoir and is pressurized by an overlying volume of pressurized air in an efficient way to promote an acceptable flow of ink from the pen during a line drawing procedure.
In keeping with this general object, a more detailed object of this invention is to provide a plotter wherein the overlying volume of pressurized air is pressurized by an air pump driven by the same motor as used to advance paper web or other sheet material which is drawn on by the pen over the support surface.
A further object of the invention is to provide an improved air pump, of simple inexpensive construction, particularly well adapted for use with a plotter of the type mentioned in the preceding paragraph for pressurizing the air overlying the ink in the ink reservoir, and which pump is capable of keeping such air adequately pressurized even though driven only periodically when the paper is advanced.
Another object of the invention is to provide a plotter with an ink reservoir wherein the ink is pressurized by an overlying volume of pressurized air and including a simple means for providing a signal indicating an "out of ink" condition, which signal may be used to operate an associated indicator or warning device and/or to interrupt further operation of the plotter.
Other objects and advantages of the invention will be apparent from the following description of detailed embodiments of the invention and from the accompanying drawings and claims.